Doug,
Jesus Christ on a bicycle, I said I agreed with you! Wha tha?
ps George, very interesting page!
meecrafty,
Thanks for the support 
daddio,
I think I know where you are coming from now. At the risk of being accused of getting caught up in a shitfight I’d like to comment on where I think we have our wires crossed.
> Energy?
Just standing up in the morning, at my age, takes all I have.
Ahmen, brother. Sounds like you are maybe only a year or two older than me
Maybe we should look at energy creation a little more creatively.
I think you are talking “energy creation” as in “making” electricity.
Picture a new road system, one that is flexible, maybe built out of Bamboo or Composite skin and it is sprung to a height above the earth so that
each time a car passes over, the weight (of our fat asses) pushes down, spins up a whatever the f–k those things are called, and stores the
energy for use by the city. What is the useable combined mass of the population that travels to and fro, by car, in a system like that on a daily
basis?
If such a thing could be done it would be great. But that is not “creating” energy. It is capturing wasted energy. Every single thing you list is fuelled by other energy. All those cars driving around are fuelled by fossil fuels which grew millions of years ago as plants powered by the sun.
Just standing up and moving around and resisting gravity, you are creating more potential energy than you know what to do with, but we’ve been
sold a crock and that is there is only one way to (extract) energy from a system (burn it) There is more than one way to skin a cat, to those that
are awakening, and we should start to consider and utilize, more effectively, our roles in the community of the earth. The dynamic abilities of our
brains and bodies have not been tapped - just to make very few rich beyond imagination.
You are not creating energy. Your body motion is fuelled by food, which is grown using the sun.
And yes, we have been sold a crock. We have been undervalued. For decades (since World War 2, to the best of my knowledge) the Oil Companies have supressed all alternative sources of energy (energy source is very different to creating energy). There have always been more efficient energy sources and less wasteful ways of using existing mainstream energy sources.
> The flapping of butterfly wings in my front garden affects the weather in your neck of the woods? Yes or no? Does the bow or the arrow or you
create and release energy?
Frequent misquote (the butterfly thing). That’s a “systems” analogy for how sensitive large, complex systems are. Very smal, almost immesurable, forces can catalyze changes which seem to be way out of proportion to the energy expended. But that is also not “creating” energy. But it highlights how energy can (should) be used in a more productive and less wastful manner.
I’m spent… gonna transfer my ass to work.
Just done the opposite.
ps George, very interesting page!
Agreed.
-doug
shitfight?
Better shut up?
Calm your jets, bro.
This is for those that might be stimulated to look into strange attractors and harmonic oscillators, not as a comment on our conversation, or lack of understanding each other.
Strange Attractors
Well this really came from a paper that I gave called “Can the flap of a butterfly’s wings in Brazil stir up a tornado in Texas?” (Actually the title was one that someone had given to me. I probably would have picked a seagull instead of a butterfly. It works the same way.) I pointed out at the beginning of the talk that this wasn’t really supposed to be a facetious question. And that if it were true then certainly if a butterfly’s wings could stir up a tornado, then a butterfly could be equally effective in preventing a tornado that otherwise would have happened… So the real question was can very small influences lead in due time to very big changes? But it’s apparently because of the title of this paper that it’s become known as the butterfly effect. (Peitgen)
A butterfly was chosen as its effect on atmospheric dynamics must surely be small and a tornado was chosen as its meteorological size is about as extreme as one can get. Extremely small perturbations in a system may result in an outcome as large as the difference between a tornado occurring or not occurring. What is informally known as the Butterfly Effect is more properly known as sensitive dependence on initial conditions (usually shortened to sensitive dependence). It is an essential characteristic of a chaotic system. Sensitive dependence is chaos.
Sensitive Dependence on Initial Conditions as illustrated with Lorenz’ Equations (from Peitgen). When the results of the eleventh iteration were truncated the equations evolved in a much different manner.
Most of the kneeboards I’ve built and ridden over the past 36 years have incorporated flex, and along the way I’ve done some thinking about what flex does. That’s not to say that my perspective is correct (I’ve certainly been wrong before), but I thought I’d present some of my reasoning anyhow.
The first point of view that I’d like to present is that the storage and release of flex, per se, has a minimal beneficial effect on the speed potential of a board, but, incorrectly done, can have an adverse effect.
The argument…
The speed that can be achieved represents a balance between the propulsive force and the drag force. In the absence of the conversion of stored energy in the system (e.g. ATP) into a propulsive force (e.g. the rider “pumping” the board), the propulsive force driving a board is determined by the weight of the rider, the force of gravity, and the slope of the sea surface in the immediate region of the wetted surface of the board. Since the first two are fixed, the only remaining variable available to the rider is where he positions himself on the face of the wave.
Examination of carefully selected pictures of surfboards being trimmed for maximum speed without direct energy input other than from gravity and the wave indicates that the slope of the wave face in the immediate vicinity of the board is typically about 45 degrees (1:1 slope). However, it is the slope along the pathline of the board that determines the propulsive power, and this slope depends on the path of the surfer relative to the onshore motion of the wave.
Scarfe, et. al. (http://www.asrltd.co.nz/3rdScarfe1.pdf) report measusrements of the actual (i.e. real) angles between a line paralleling the crest of a wave and the pathline (over the bottom) of the surfer and board in their studies of the characteristics of desirable surf breaks. For moderate size waves, the minimum included angle (maximum speed under steady-state conditions) was found to be about 35 degrees (increasing a bit as the wave size increases). To a first approximation, for a wave face slope of 45 degrees, and steady-state conditions (i.e. the surfer has achieved his maximum steady speed) this results in a wave face slope along the pathline of the craft of about 0.574 (or a pathline slope angle of 29.8 degrees).
Since by definition the lift force is perpendicular to the free stream velocity by the board, and the drag force is parallel to the free stream velocity, for a surfer (and board) with a weight of 165 lbs, the drag force can be shown to be:
Fd = W * sin (pathline slope angle) = 165 * sin(29.8 deg) = 82 lbs.
where:
Fd = drag force (lbs)
W = combined weight of the surfer and board
The power which is being dissipated (and which is supplied by the wave and gravity) is given by the equation:
P = Fd * V
where:
P = power dissipated
V = speed of the craft over the water
I have collected 50+ measurements (via GPS) of the maximum speed attained during individual surf sessions in waves ranging from waist high to double overhead. Most of the measurements were on head high breakers, with a shortboard or kneeboard, and at Swamis. The session maximum speeds averaged 19.5 mph ( or 28.6 ft/sec). The standard deviation was 1.6 mph. For this average session maximum speed, the power being dissipated is then:
P = Fd * V = 82 lbs * 28.6 ft/sec = 2348 ft-lb/sec = 4.27 hp
where:
P = power being dissipated
V = speed of the craft across the water
The well trained athlete can momentarily generate on the order of 1 hp. Half that is more representative of a more sustained effort by a fit person. Assuming the latter, the power supplied by the surfer could potentially add approximately 9.4 percent to the total power available to the surfer/board/wave system. How much of this can be converted to a propulsive force depends on the efficiency of the transfer mechanism. Let’s assume 100-percent efficiency. Furthermore, let’s assume that the board is going sufficiently fast that induced drag is small comparison with the parasitic and form drag. In that case, the drag force increases as the square of the speed across the water. Thus with the addition of energy from the surfer, the new maximum speed, V’, that can be achieved can be computed from the equation:
P’ / P = (1+0.094) = (V’/V) * (V’/V)^2 = (V’/V)^3
from which it follows that:
V’/V = cube-root (1.09) => 3.0 percent increase
In short, the speed would be increased by about 3 percent (at 100-percent transfer efficiency of the 0.5 hp supplied by the rider).
How might this power be converted to a propulsive force? One commonly suggested means is to weight and unweight the board such that the tail (or rocker) of the board flexes up and down (sort of the surfing equivalent of sculling with a tiller). So next let’s compute a rough estimate of how much power might be stored and released in a hypothetical flexing surfboard. For the sake of this illustration, let us assume that the board bends such that the position of the board under the surfer sags down 4 inches (relative to the nose and tail) when the surfer stands on the board (less flex for the same weight means less stored energy; more flex means more stored energy). The flex of the board is given by the equation:
F = K * Z
and the energy stored in the flex is:
E = (1/2) * K * (Z)^2
where:
F = applied force (165 lbs, in the absence of pumping)
E = the stored energy (ft-lbs)
K = spring constant (lbs/ft)
Z = vertical deflection (1/3 ft)
The spring constant, K, can be computed from the force equation, and yields:
K = 165/(1/3) = 495 lb/ft
The energy stored in the flex when the surfer steps on the board (1g loading) is then:
E = (1/2) * (495) * (1/3)^2 = 27.5 ft-lbs
Now let’s assume that the surfer “pumps” the board by pushing down with his feet to load the board to “2 g’s” and the flex increases to 8 inches (2/3 ft). Then he unweights the board so that it returns to its unstressed state (deflection = 0 ft). The energy stored in the latter (undeflected) state is 0 ft-lbs; the energy stored in the fully flexed state is 4 * 27.5 lbs = 110 ft-lbs.
Let us further assume that he cycles through the compress/uncompressed sequence two times a second. The power he is putting transferring into the board via the flex is then:
P = 110 ft-lbs/0.5 sec = 220 ft-lbs/sec = 0.4 hp
This is close to our earlier assumption of a moderately sustained power of 0.5 hp. Moreover since there is dampening in the flexing of a surfboard, which reduces the power transferred, the actual transfer might be even less than 0.4 hp.
Now it was shown earlier that this additional power might increase the speed attainable by the 100-percent transfer of power to a propulsive force by about 3 percent. However, it is highly likely that the transfer efficiency for this type of motion is much less than 100 percent. For example, I can achieve a short-term static thrust using (only) swim fins of about 27 lbs, but about 35 lbs with webbed gloves (and no fins or kicking)—even though a person’s legs are capable of supplying much more power than the arms. That’s because the arm stroke mechanics and hydrodynamics are much more efficient that those of the kicking stroke and fins. Our surfboard flex example mimics the kicking with swim fin motion much more closely than it does the arm stroke motion, giving a pretty good indication that this type of surfboard flex is not a very efficient means of transferring the energy input into the system by the surfer in order to to add to the propulsive force. I would be surprised if the efficiency even approached 33 percent, and hence one might expect that the combination of pumping a flexible board in this manner might, at most, increase the speed by about 1-percent. A more efficient transfer mechanism probably occurs when the surfer “pumps” the board by making a series of alternating “turns” similar to a skating motion (note that this move is not necessarily strongly dependent on board flex). But even then, the analysis above indicates that the speed increase is still likely to only be on the order of 1 to 3 percent.
However, this analysis should not be interpreted to mean that pumping (especially in the “skating” mode) can not have a beneficial, and even a critical effect, on the ability to make a wave. But I believe that this is because it can reduce the time required to accelerate to maximum speed. As noted above, at “high planing speeds”, the primary source of drag is parasitic (skin friction) and form drag—both of which increase as the square of the speed.
However, at “low planing speeds”, the primary source of drag is the induced drag (associated with creating sufficient lift force to maintain the surfer and board on the surface of the water). This drag increases as the square of the inverse of the speed over the water (i.e. going half as fast increases the drag by a factor of four). Hence if one starts out in this “low speed” state, as one accelerates to a higher speed the induced drag (and hence the total drag) will decrease. This, in turn, frees up even more net propulsive power (i.e. the difference between the total propulsive force and the drag) and results in an increasing acceleration.
Hence any increase in propulsive force via the pumping input from the rider can enhance the acceleration, and this increase can have a snowballing effect on the overall acceleration—at least up to the point where parasitic and form drag become comparable to the induced drag. At speeds above that point, the effects of pumping will diminish. But in the mean time, the time and distance required to “get up to speed” may be substantially less than if the rider had not “pumped” the board.
In summary, it appears that the dynamic storage and release of energy in the flex of a board yields very little beneficial effect on the maximum speed that can be achieved on a wave.
That is not to say, however, that flex cannot have beneficial consequences from a quasi-static change in the hydrodynamic properties of the craft (as opposed to the energy stored by flexing and unflexing). For example, on flat water the fastest planing hulls (excluding hydroplanes, etc.) tend to be those with the equivalent of no, or very little, “rocker” in the wetted surface.
A first order approximation to the equivalent condition on a surfboard would seem to be a board with “natural rocker” --i.e. the rocker in the board matches the curvature of the wave face within the wetted region of the board. Note that this natural rocker is dependent on the position of the board on the wave face, and the included angle between the crest of the wave and the pathline of the craft (increasing as one goes “straight off” and approaching virtually no rocker the faster one races across the face of the wave). Hence one possible means of using rocker to increase the speed of a board is to develop a structure that conforms to the wave face in the vicinity of the board AND satisfies the requirements that:
(1) the dot product of the normal to the sea surface with the integral of the pressure force over the wetted area equals the required lift force
(2) and the dot product of the vector integral over the total wetted area of the hull of the local pressure force with the free stream velocity vector is a minimum
…for all important positions on the face of the wave.
In my opinion the primary advantage of flex in a kneeboard is in facilitating maneuvering–and this is the basis for the “flex-rail” design that is incorporated into virtually all of my flexing kneeboards (some of which have been posted here previously).
mtb
hi mtb…interesting analysis but help me connect some dots as your analysis is based on a few assumptions…
you mention pumping in standup surfing a lot but your conclusion about knee boarding doesnt directly address it…assuming the board is made ‘right’ and the surfer loads into a bottom and includes some pump (banking the bottom of the board off the water)…cant the surfer use the board’s pop (flex return) to create some added boost out of the turn?
you can load the board more slowly into the BT but the surfer has the option of unloading it quickly…energy transfer…you can carve (kneeboard style or classic surf style) or you can drive out of that BT with some added boost from the right combination of style, ability and engineered flex…the degree of boost from a pump is very board dependent…my opinion, but its safe to say that there are very few surfboards out there that truly flex/boost/transferE with good efficiency…comments?
also, the 4-8 inch flex assumption seems a bit odd when you consider pumping is mostly shortboard specific…just cant see the benefit to flexing that much unless you really want a tight arc or want to slow down dramatically
when i first tried parabolic snow skiis i didnt necessarily ski better (although that can be argued) but man did those skiis feel good to ride…so to add to your conclusion but more standup shortB specific, flex return particularly if you could generate a stronger return via ???..can have a significant benefit…but it just might be that the benefit is not better but only different…different in a very positive way
Hey daddio!
shitfight?
Better shut up?
Calm your jets, bro.
LOL! This medium conveys tone very poorly. That’s why the various emoticons, acronyms and E-xpressions (intentional capital and hyphen) were developed. Been on the net since the late 80s and on BBSs before that. Seen alot of flame wars and I generally try to avoid them, hence my comments.
Gotta agree with your short take on Chaos Theory My point was that it doesn’t have anything to do with creating energy and that energy can only be stored and released. And I think that’s what we need to be looking at regarding flex in surfboard design.
-doug
Remember that pumping a shortboard (tri-fin) is not about flexing hulls, its about fins or lift from rail shape. I’ll admit there is an illusion of push/squirt/rebound when turning a flexable board but I’m now convinced that I was really feeling a lack of decelleration afforded by the board flexing back to a flat rocker. It was about more efficient planing.
Hey MTB!
NICE analysis mate! So flex and energy transfer (to the board) aren’t necessarily an optimal way to go… Must admit that the main reason I have personally been thinking along the flex lines has been due to the comments on responsiveness and durability I have read. If I read you right you aren’t disagreeing with that.
-doug
Hey, Doug!
Excellent post, I loved the way you subtly put me in such a pleasant light, and marvel at the fluency of your positive words.
I have such high hopes that you will read about harmonic oscillators and dampeners and vibrational frequencies and on and on so we can have a jolly good discussion. Not you, but there is a conforming clique that tries to make everything follow in a linear fashion where none exists. Comparisons do not necessarily work at the next level, DYNAMIC flex/return and PASSIVE flex, to which the Velo and mat are the most advanced members. George, when you described the methods of riding the Velo and how you use your body to dynamically shape and form your craft, my mind was blown. It is one thing to see pictures but to feel the AMOUNT of flex is mind bending. All my friends, I implore you, please read about harmonic oscillators and you will see for yourself how physics has left a crack in the door to magnify>energy, oh I said it again, I feel so naughty, somebody spank me.
The pumping that the flex-heads are talking about, is not a bottom turn squirt thing, it is a dropping and rising, dropping and rising on the wave face. Truly a “magic carpet” ride that I’m beginning to see more clearly in my minds eye.
Three categories(?):
The fin - tail/edge riders.
The hull and entire surface planing/rail riders.
The flexible membrane riders.
Thanks for listening, good night and God bless you, you’re the best…
If I may -
Among the nice things about flex in a planing hull is that not only can it assume a more useful curvature in a turn, but inherently have the ability to assume a rocker that’s paralell to the water surface and thus minimising drag. Little or no distortion of the path of the water flowing along the bottom. This goes some way towards describing how low pressure mats ( a’ la’ Solomonsen) have such nice speed characteristics: they skim on top of the water surface by conforming to it.
Using a planing surface without flexibility, especially on a curved water surface ( a wave) , finding a position where the curvature of the surface coincides with the curvature of the planing surface is more or less a happy accident ( give or take operator skill) . This position does not necessarily coincide with the fastest path along that surface. Moreover, compromises made in the rigid planing surface to facilitate turning, etc, compromise the ability of that surface to work in those parts of the wave which can provide the greatest speed.
Now, ‘pumping’ a board may have some utility in small, inconsequential ‘contest’ waves, where the power available from the wave itself is so little that any added power would be of use, but that’s kinda irrelevant.
doc…
Hey MTB,
Very nice.
For analysis sake you have really nailed the
formulas and applications. I prcessed a lot of these things years ago with the hel of my brother. But you have taking other things into account. I never really got into the flex issue. So since you have and you have very clear thoghts about this I’m wondering if we can plug some different numbers into your system?
For this I would go back to observation step. It appears to me that Slater at Chops a few months ago got his perfect tens by riding as high on the face as he humanly could. From that information as as 1st step I was wondering if we could go back and look at the wave face angle and try differnt numbers. And see if it changes the form or direction the analysis takes. See I base this on the fact that a wave face has different places with different angles. Those angles range from flat in front to 90 degrees to past 90 as the wave forms a jet. I am presuming that the pump is to get to that part of the wave that is most verticle because that is “where the speed is”. And the the pump is not necessarirly a flex power issue. Or if there is some springbord effect from the board what suggestions would you have to how muuch spring?
Pros tell me that whatever speed a rider can obtain from a wave is in the top 1/2 for some waves, the top 1/3 for others, and the top 1/4 on the slopeiest waves like in CFL. Understnding this small minute bit of info helps a top surfer determine how and what gear he will ride on any given day. It is perhaps the information that separates the top surfers from the rest. But I digress.
How, if you could, would you incorporate this information into your thinking. Thanks take you time. Pleasure reading your work. m
OK, here’s a real quick one that you may be missing.
You’ve seen how this board flexes and morphs:
http://flexspoon.com/pics/all_flex/index.html
What if the board has been properly designed so that as it moves faster over the water it flexes/morphs into a more aero/hydrodynamic efficient shape, reducing drag?
So everytime it comes out of a flex/pump/spring turn it
-
gains a little speed which
-
alters board into “speedier” shape reducing drag and allowing greater speed leading into next flex/pump/spring turn
If you measure the drag of a dead, stiff tuna you will get one reading, a live, flexing, morphing tuna might give you some/many others. The fish “feel” what is going on and adjust accordingly.
Didn’t Greenough figure out a lot by watching fish?
Didn’t Greenough claim that Velo had “unlimited gears”?
That is what he was talking about.
Hey Other George,
I’m not sure I have the vocabulary to treat this subject properly.
Also this is a little different or off subject from my post, but you’re on a point that is interesting.
I think maybe some things are going on that are not included in any of the above explainations. Within that maybe things could be explained a little clearer. I will try and make my point.
Is maybe the membrane morphing actually a shock absorber?
Instead of transitioning uneven water surface energy into bounce it is absorbed by the bottom and returned when the other side of the bump is reached. This would tend to keep the bottom attached to the wave surface as the board travels over it. Staying attached to the flow is a valid design feature goal when trying to maintain speed and control. So yes I see the flex in that membrane as a good thing, I just think it may be working is ways that are different than the ways they are being discussed here. Or maybe they are less of a contributing factor.
However I also understand those ways too. And they may be working too simultaneously. I just think more thought can be put into understanding ALL the things going on at once.
Also, is there a hierarchy of purposes. Shock abosrber first. Other purposes relative and subjective or secondary and happening after and with less energy flow interruption or transfer following after that. m
Or maybe visualize it this way. A motocross rider will adjust his speed to just hit the tips of the bumps. It’s a combination of springs shocks timing ans skill. But he can go faster than if he were to feel the full impact of each bump going up and down each.
So the board goes level while the membrane follows the contour. Dont hold me to any of this. I’m still working on my visualization…trying to catch up. I have been working my way through MTBs math.
Mark,
Shock absorber - yes that is yet another aspect. Better yet - suspension - shocks, springs and geometries. Because I raced cars I am familiar this. A properly tuned suspension will keep the wheel in contact with the ground by dampening bumps and dips. Watch rally cars, offroad vehicle and motocross. The suspensions now just soak up the bumps and dips.
Even better - “active suspension”. In a racecar controlled by sensors and computers.
I’m appreciating Greenough more and more…
In Nascar they set a “minimum spoiler angle” to keep the cars equal and hold down speeds on tracks like Taladaga and Daytona. If they laid the spoiler farther back(less drag) the cars went too fast.
Nascar guys got smart and made flexible rear spoilers that were upright at low speeds and when measured by officials.
At higher speeds the spoiler would flex and lay back allowing higher speeds! There is now a stiffness requirement for spoilers in Nascar.
Jim Hall and his Chaparral had a driver adjustable rear wing for the same purpose starting in 1966 - more drag when needed for braking and low speed turns - less drag for high speeds. Adjustable. I think he had a catastrophic failure when a wing support collapsed.
Adjustable aerodynamic devices are banned in most(all?) forms of auto racing.
Yes, suspension. Think along those lines.
Now if you wanted to race tune it you could take a
round, square, rectangular, or triangular aluminum tube, bend it into the horseshoe shape and build it into the foam.
Because the twisting is counter productive.
Or, I wonder if anyone is doing this, but you could laminate about three vertical pieces of balsa and make a rail. Hmmm…
Daddio,
Perimeter stringer, yeah, good one. Thought about that after I posted. Too busy playing Jeopardy and watching New Orleans to get back online. YOU beat me to the post:-)
Must be some good ideas if they are inspiring other ideas.
Funny how fast they grow once the level of understanding
is commonized.
I wonder if this is being done in body boards?
I know they have perimeter stringers, but not if they have imbedded ones. Guess I could check. m
Mark said:
Quote
Because the twisting is counter productive.
and I’ve read this many times before from others. Please explain. Counter productive related to what?
It was only when I came to Swaylocks and KSUSA that I read/learned twisting was bad.
I have experienced many inches of twist in a 5’ long board as a great thing. The twist allows the board to assume the shape of the wave. And I can initiate a turn with the front of the board while the tail is still flat and going straight. This can really “load up” the board and help/cause it to carve a tighter arc. This is where the flex/return spring comes in. Part of the spring is in the “untwisting”? So the twisting into a turn causes longitudinal flexing/rocker changing as the tail is forced to chase the nose. When all this is “released” the board untwists and springs flat(or more).
the frame - yes except I want a frame that does twist.
Just pulling up on one corner of the front does not guarantee the cross corner will go down. Now what are you making a body board knee board or surfboard? If pushing down on a rear corner you want the rail of the same side to hold down not rise up. If you are connected to the cross corner with some sort of rigid mechanical device like a perimeter stringer or internal frame it will pull up the cross corner as you drive down the rear corner and drive the inside front rail down and help turn. So whether you are pulling up on the front or pushing down on the rear you want a connection that will result in controlling the opposite corner. That is where turn control is.
Not really happy with my explanations lately. Hope this makes sense.